Process for making crosslinkable polyurethane/acrylic hybrid dispersions

ABSTRACT

The present invention provides a new process of preparation for PUA with superior mechanical performance, such as elongation, and tensile strength. The process is solvent free, smooth, and robust. PU prepolymer prepared according to the present invention has low viscosity, and contains no particulate DMPA.

FIELD

The invention relates to a new process for making crosslinkablePolyurethane/Acrylic (PUA) hybrid dispersions, specifically, it relatesto a chemical hybrid method for preparing stable crosslinkable PUAhybrid dispersions and the crosslinkable PUA hybrid dispersions producedby this process.

BACKGROUND

Over recent decades, there has been a concerted effort to reduceatmospheric pollution caused by volatile solvents which are emittedduring painting processes. Due to environmental concerns, volatileorganic compounds (VOCs) have come under strict regulation by thegovernment. Therefore, one of the major goals of the coating industry isto minimize the use of organic solvents by formulating waterbornecoating compositions which provide a smooth, high gloss appearance, aswell as good physical properties including resistance to acid rain.While the solvent-type coatings provide many benefits, such as that theyare fast-drying, have a high hardness, a high abrasion-resistance, ahigh water-resistance, a high chemical-resistance and a low price, thewaterborne coatings have environment-friendly benefits in that they arenot flammable or explosive. The waterborne coatings use water as thesystem solvent and contain no poisonous chemicals. They require no orlow amounts of volatile organic compounds.

The unique advantage of polyurethane dispersions (PUDs) in relation tosurface coatings is their ability to form coherent film and to controlthe microphase morphology by controlling the relative amounts of softand hard segments in polymer chain. These features allow PUDs to beemployed in a wide variety of surface coating applications wheremechanical properties are particularly crucial. High abrasionresistance, superior toughness, elastomeric properties, and highextensibility at low temperature are typical benefits. However,relatively high raw material cost in comparison with a typical acrylicemulsion has restricted its use in many industrial applications. Toovercome this, polyurethane dispersions have been combined with otherrelatively inexpensive polymers to obtain a cost/performance balancebecause the properties of polyurethane (PU) and the polyacrylate (PA)complement each other. The composite materials of PU and PA are moreoutstanding in terms of adhesion, film-formability, non-stickiness,weather-resistance, elongation and strength of the film with excellentcost-performance balance. Accordingly, since the development of PU, themodification of the PU by the PA has been an active research topic inthe art.

Two methods can be used to modify PU with PA: physical methods andchemical methods. The physical method is achieved by mechanical mixing.In the physical method, aqueous PA and PU dispersions (emulsions) areindependently prepared first, and then both dispersions are mixedtogether under mechanical power. It is a very convenient method thatmakes it easy to control the composition of the final product. However,in such blends the superior performance properties may be compromisedbecause of the incompatibility of the two. Such blended dispersion maysuffer from instability.

For these reasons, the chemical modification technology currently playsa more important role. The chemical method is achieved bypost-polymerization of acrylates. In the chemical method, the PUdispersion can be prepared first, and then acrylates and other vinylmonomers can be polymerized in the PU dispersion. In most cases,core-shell emulsion polymerization is adopted. PU particles are used asseed particles and the acrylates are polymerized within the PU particlesdue to high hydrophobicity of the acrylates. These hybrid dispersionsare expected to provide the advantages of PA, such as excellent weatherresistance, affinity to pigments as well as lower cost, and theadvantages of PU, such as better mechanical stability, excellentadhesion, solvent and chemical resistance, and toughness.

U.S. Patent Application No.: 2009/0111934 A1 to Caideng Yuan disclosesmethods for the preparation of an aqueous PA modified PU dispersion,which includes three main steps: a) preparation of PA polymer orcopolymer dispersion; b) preparation of PU prepolymer with carboxylicgroups and neutralization treatment to the carboxylic groups; and c)dispersion and chain-extension of PU prepolymer by adding the PAdispersion into the PU prepolymer under vigorous agitation, or othermechanical operation. The result hybrid dispersion can beself-crosslinked by reaction between acetoacetoxy compound on PAparticle and amine group on PU dispersion particles. A solvent,N-methyl-2-pyrrolidinone (NMP, b.p. 202-204° C.) was used as during thePU dispersion synthesis process. The use of NMP raises environmentalconcerns.

U.S. Publication No. 2004/0034146 discloses a complicated solvent freeprocess for preparing hybrid PUA. The PU prepolymer was NCO free andthere is no chain extension step in water. The viscosity of the PUprepolymer could be too high to be well dispersed into water.Additionally, dimethylol propane acid (DMPA) was used as an acidcontaining diol which provides water-dispersity of the PUA dispersion.However, DMPA is hard to dissolve completely, so that the finalprepolymer may still contain particulate DMPA and the reaction was notcomplete.

The present inventors have solved the problem of inhomogeniety of thereaction system and have provided processes for preparing PUAs withsuperior mechanical performance, such as elongation, and tensilestrength. The process is solvent free, smooth, and robust. PU prepolymerprepared according to the present invention has low viscosity, andcontains no particulate DMPA.

SUMMARY

The present invention provides processes for making polyurethane/acrylichybrid dispersions comprising: i) adding at least one polyol to areactor; ii) adding DMPA simultaneously with/after step i), but beforestep iii), as water dispersibility enhancing agent at a temperature offrom 115° C. to 140° C. to obtain a homogeneous solution; iii) adding atleast one polyisocyanate at a temperature of from 75° C. to 95° C. untilthe NCO content reaches a constant value to prepare the polyurethaneprepolymer; iv) adding at least one acrylate monomer(s), at least onestyrenic monomer(s), or the mixture thereof, as diluent to thepolyurethane prepolymer, at a temperature of from 40° C. to 65° C.; v)adding neutralizing agent; vi) dispersing and extending the polyurethaneprepolymer in the presence of the acrylate monomer, and/or the styrenicmonomer of step iv); and vii) adding at least one ethylenicallyunsaturated nonionic monomer(s), and co-polymerizing the same with theacrylate monomer, and/or the styrenic monomer of step iv), to get thepolyurethane/acrylate hybrid dispersion. The process is continuous.

The present invention further provides processes for makingpolyurethane/acrylic hybrid dispersions comprising cold-blending thepolyurethane/acrylic hybrid dispersions of the present invention withpolyacrylate dispersion under agitation. Optionally, thepolyurethane/acrylic hybrid dispersion and polyacrylate dispersion areboth modified by copolymerization with diacetone acrylamide (DAAm) oracetoacetoxyethyl methacrylate (AAEM).

Further, adipic acid dihydrazide, as crosslinker, may be added into theblend.

The present invention further provides the polyurethane/acrylic hybriddispersions prepared thereof.

The present invention further provides a coating composition comprisingthe polyurethane/acrylic hybrid dispersion prepared thereof.

DETAILED DESCRIPTION

In the present invention, the term “polyurethane” or “PU” describespolymers including oligomers (e.g., prepolymers) which contain multipleurethane groups, i.e., —O—C(═O)—NH—, regardless of how they are made. Asis well known, polyurethanes can contain additional groups such as urea,allophanate, biuret, carbodiimide, oxazolidinyl, isocyanurate,uretdione, ether, ester, carbonate, etc., in addition to urethanegroups. Typically, the prepolymers will be above 1,000 or 2,000 Daltonsin number average molecular weight and if the chain is extended duringprocessing, can reach number average molecular weights in the millionsof Daltons.

The term “polyacrylate” or “PA” as used herein means those polymers orresins resulting from the polymerization of one or more acrylates suchas, for example, methyl acrylate, ethyl acrylate, butyl acrylate,2-ethylhexyl acrylate, etc. as well as the methacrylates such as, forinstance, methyl methacrylate, ethyl methacrylate, butyl methacrylate,hexyl methacrylate, etc. Copolymers of the above acrylate andmethacrylate monomers are also included within the term “polyacrylate”as it appears herein. The polymerization of the monomeric acrylates andmethacrylates to provide the PA dispersions useful in the practice ofthe invention may be accomplished by any of the well knownpolymerization techniques.

PUA in this invention is prepared by a) PU prepolymer preparation; b)dispersing and extending PU prepolymer in water; and c) adding andpolymerizing at least one ethylenically unsaturated nonionic monomer(s).

In a), PU prepolymer preparation of the present invention is conductedunder decreasing temperature. Polyol(s) is added into the reactionvessel (the system) under N₂ purging and the system is heated to a hightemperature, preferably from 115° C. to 140° C., more preferably from120° C. to 130° C. DMPA, as a water-dispersibility enhancing agent issimultaneously or later added into the system under mild stiffing untila homogeneous solution is obtained. System temperature is lowered to 75°C.-95° C., more preferably from 80° C. to 85° C. Polyisocyanate(s) isthen added into the system, and the reaction proceeds until the NCOcontent reaches a constant value. After that, temperature is loweredfurther to from 40° C. to 65° C., more preferably from 55° C. to 60° C.,and at least one acrylate monomer(s), at least one styrenic monomer(s),or the mixture thereof is added as reactive diluent or so calledsolvent. The weight ratio of acrylate and/or styrenic monomers in thetotal weight of prepolymer could range from 10 wt. % to 50 wt. %,preferably from 10 wt. % to 30 wt. %. Following that, triethyl amine(TEA) as neutralizing agent is added. The molar ratio of TEA to DMPAranges from 0.9:1 to 1.1:1, preferably from 0.9:1 to 1:1.

In b), after a short (several minutes, such as, from 5 to 15 minutes,etc.) mixing time, the prepolymer is gradually poured into DI waterunder agitation to form a dispersion. Several minutes later, chainextender with a molar ratio to NCO as 0.9:1 to 1.1:1, preferably from0.9:1 to 1:1 is added dropwise to above dispersion.

Then, ethylenically unsaturated nonionic monomer(s) is added into thesystem as polymerization unit. The total amount of ethylenicallyunsaturated nonionic monomer(s) is from 10 wt. % to 80 wt. %, preferablyfrom 30 wt. % to 50 wt. % basing on the total weight of the PUA polymer.

The dispersing b) can alternatively be conducted by pouring the PUprepolymer into a PA dispersion under agitation followed by chainextension.

In c), at least one ethylenically unsaturated nonionic monomer(s) isadded and then polymerized via radical polymerization in the presence ofinitiator and at elevated temperature.

Optionally, the PUA dispersion prepared according to the above processcan be mixed with PA dispersion under agitation.

Optionally, the PUA dispersion and PA dispersion are separately modifiedby copolymerization with diacetone-based monomer, preferably, with DAAmor AAEM and other acrylate monomer(s). The amount of DAAm or AAEM isaround 1 to 3 wt %, based on the total weight of monomers used to makethe acrylic/styrenic portion of PUA.

Adipic acid dihydrazide (ADH), as crosslinker, may be added into to theblend of PUA and PA dispersions. The content of polyacrylate, includingthose in both PA and PUA, may range from 10 wt. % to 80 wt. % in thetotal weight based on the total solids of PA and PUA.

Polyols, including polyether diols, polyester diols or multi-functionalpolyols, are used to prepare the PU prepolymer. “Polyols” means anyproduct having two or more hydroxyl groups per molecule. Non-limitingexamples of the polyols useful herein include polyether polyols,polyester polyols such as alkyds, polycarbonate polyols, polyhydroxypolyester amides, hydroxyl-containing polycaprolactones,hydroxyl-containing acrylic polymers, hydroxyl-containing epoxides,polyhydroxy polycarbonates, polyhydroxy polyacetals, polyhydroxypolythioethers, polysiloxane polyols, ethoxylated polysiloxane polyols,polybutadiene polyols and hydrogenated polybutadiene polyols,polyisobutylene polyols, polyacrylate polyols, polyols derived fromhalogenated polyesters and polyethers, and the like, and mixturesthereof. The polyether polyols, polyester polyols, and polycarbonatepolyols are preferred.

The polyether polyols that can be used as the active hydrogen-containingcompound according to the present invention contain the —C—O—C— group.They can be obtained in a known manner by the reaction of startingcompounds that contain reactive hydrogen atoms such as water or diols,and alkylene oxides such as ethylene oxide, propylene oxide, butyleneoxide, styrene oxide, tetrahydrofuran, epichlorohydrin and mixturesthereof. Preferred polyethers include poly(propylene glycol) withmolecular weight of 400 to 3000, polytetrahydrofuran and copolymers ofpoly(ethylene glycol) and poly(propylene glycol). The diols used in thepreparation of the polyether polyols include alkylene glycols,preferably ethylene glycol, diethylene glycol and butylene glycol.

The polyester polyols are typically esterification products prepared bythe reaction of organic polycarboxylic acids or their anhydrides with astoichiometric excess of a diol or diols. Non-limiting examples ofsuitable polyols for use in the reaction include poly(glycol adipate),poly(ethylene terephthalate) polyols, polycaprolactone polyols, alkydpolyols, orthophthalic polyols, sulfonated and phosphonated polyols, andmixtures thereof. The diols used in making the polyester polyols are asset forth for preparing the polyether polyols. Suitable carboxylic acidsused in making the polyester polyols include, but are not limited to,dicarboxylic acids, tricarboxylic acids and anhydrides, e.g., maleicacid, maleic anhydride, succinic acid, glutaric acid, glutaricanhydride, adipic acid, suberic acid, pimelic acid, azelaic acid,sebacic acid, chlorendic acid, 1,2,4-butane-tricarboxylic acid, phthalicacid, the isomers of phthalic acid, phthalic anhydride, fumaric acid,dimeric fatty acids such as oleic acid, and the like, and mixturesthereof. Preferred polycarboxylic acids used in making the polyesterpolyols include aliphatic and/or aromatic dibasic acids.

Particularly interesting polyols are the polyester diols containing—C(═O)—O-group. Non-limiting examples include poly(butanediol adipate),caprolactones, acid-containing polyols, polyesters made from hexanediol, adipic acid and isophthalic acid such as hexane adipateisophthalate polyester, hexane diol neopentyl glycol adipic acidpolyester diols, as well as propylene glycol maleic anhydride adipicacid polyester diols, and hexane diol neopentyl glycol fumaric acidpolyester diols.

Polyisocyanates have two or more isocyanate groups on average,preferably two to four isocyanate groups per molecule. Polyisocyanatestypically comprise about 5 to 20 carbon atoms and include aliphatic,cycloaliphatic, aryl-aliphatic, and aromatic polyisocyanates, as well asproducts of their oligomerization, used alone or in mixtures of two ormore. Diisocyanates are preferred. Toluene diisocyanate, hexamethyleneisocyanate and/or isophorone isocyanate may preferably be used in theembodiment of the present invention.

Non-limiting examples of suitable aliphatic polyisocyanates includealpha, omega-alkylene diisocyanates having from 5 to 20 carbon atoms,such as hexamethylene-1,6-diisocyanate, 1,12-dodecane diisocyanate,2,2,4-trimethyl-hexamethylene diisocyanate,2,4,4-trimethyl-hexamethylene diisocyanate, 2-methyl-1,5-pentamethylenediisocyanate, and the like. Preferred aliphatic polyisocyanates includehexamethylene-1,6-diisocyanate,2,2,4-trimethyl-hexamethylene-diisocyanate, and2,4,4-trimethyl-hexamethylene diisocyanate.

Non-limiting examples of suitable cycloaliphatic polyisocyanates includedicyclohexylmethane diisocyanate (commercially available as Desmodur™from Bayer Corporation), isophorone diisocyanate, 1,4-cyclohexanediisocyanate, 1,3-bis-(isocyanatomethyl)cyclohexane, and the like.Preferred cycloaliphatic polyisocyanates include dicyclohexylmethanediisocyanate and isophorone diisocyanate.

Non-limiting examples of suitable araliphatic polyisocyanates includem-tetramethyl xylylene diisocyanate, p-tetramethyl xylylenediisocyanate, 1,4-xylylene diisocyanate, 1,3-xylylene diisocyanate, andthe like. A preferred araliphatic polyisocyanate is tetramethyl xylylenediisocyanate.

Non-limiting examples of suitable aromatic polyisocyanates include4,4′-diphenylmethylene diisocyanate, toluene diisocyanate, theirisomers, naphthalene diisocyanate, their oligomeric forms and the like.A preferred aromatic polyisocyanate is toluene diisocyanate.

The PU prepolymer may be formed without using a catalyst if desired, butusing a catalyst may be preferred in some embodiments of the presentinvention. Non-limiting examples of suitable catalysts include stannousoctoate, dibutyl tin dilaurate, and tertiary amine compounds such astriethylamine and bis-(dimethylaminoethyl)ether, morpholine compounds,bismuth carboxylate, zinc bismuth carboxylate anddiazabicyclo[2.2.2]octane. Organic tin catalysts are preferred.

In the present invention, organic solvents are preferably not used, sothe solvent-removing stage is omitted.

Chain extenders used in the preparation of the PU dispersion areemployed in the dispersion step b). Non-limiting examples of chainextenders useful in this regard include any of inorganic or organicpolyamines having an average of about 2 or more primary and/or secondaryamine groups, amine functional polyols, ureas, or combinations thereof,and their mixtures. Suitable organic amines for use as a chain extenderinclude, but are not limited to, diethylene triamine (DETA), ethylenediamine (EDA), meta-xylylenediamine (MXDA), aminoethyl ethanolamine(AEEA), 2-methyl pentane diamine, and the like, and mixtures thereof.Also suitable for the present invention are propylene diamine, butylenediamine, hexamethylene diamine, cyclohexylene diamine, phenylenediamine, tolylene diamine, 3,3-dichlorobenzidene,4,4′-methylene-bis-(2-chloro aniline), 3,3-dichloro-4,4-diaminodiphenylmethane, sulfonated primary and/or secondary amines, and thelike, and mixtures thereof. Suitable inorganic amines include hydrazine,substituted hydrazines, and hydrazine reaction products, and the like,and mixtures thereof. Suitable ureas include urea and its derivatives,and the like, and mixtures thereof. Ethylene diamine is preferably used.The amount of chain extender, which can be added before or afterdispersion, typically ranges from about 0.5 to about 1.1 equivalentsbased on available equivalents of isocyanate.

The PA dispersion of the present invention may comprise a homopolymer ofacrylates, a copolymer of acrylates, a copolymer of acrylates with othervinyl monomers, and/or mixtures thereof. With the consideration ofproperties and prices of the products, all traditional co-monomers maybe used to prepare the polymers and copolymers.

Non-limiting examples of suitable acrylate monomer(s) include esters of(meth)acrylic acid containing 1 to 18 carbon atoms in the alcoholradical, such as methyl methacrylate, butyl methacrylate, ethylacrylate, butyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate andstearyl acrylate; di(meth)acrylic acid esters of diols, e.g. ethyleneglycol, 1,4-butanediol or 1,6-hexanediol. The monomers including methyl(meth)acrylate, ethyl acrylate, butyl acrylate, hexyl acrylate,2-ethylhexyl acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate and glycidyl methacrylate, are preferable.

The ethylenically unsaturated nonionic monomers include, for example,(meth)acrylic ester monomers, where (meth)acrylic ester designatesmethacrylic ester or acrylic ester, including methyl acrylate, ethylacrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, laurylacrylate, methyl methacrylate, butyl methacrylate, isodecylmethacrylate, lauryl methacrylate, hydroxyethyl methacrylate,hydroxypropyl methacrylate; (meth)acrylonitrile; (meth)acrylamide;amino-functional and ureido-functional monomers; monomers bearingacetoacetate-functional groups; styrene and substituted styrenes;butadiene; ethylene, propylene, α-olefins such as 1-decene; vinylacetate, vinyl butyrate, vinyl versatate and other vinyl esters; andvinyl monomers such as vinyl chloride, vinylidene chloride.

Herein, “nonionic monomer” means that the copolymerized monomer residuedoes not bear an ionic charge between pH=1-14.

For the polymerization of monomers, initiators may be used. Examples ofsuitable initiators include, but are not limited to, peroxides such aspotassium peroxy-disulphate, ammonium peroxydisulphate, organicperoxides, organic hydroperoxides and hydrogen peroxide. Redox systemsare preferably used, such as water-soluble, radical-producingnon-ionogenic peroxides, e.g. t-butyl hydroperoxide, as the oxidationcomponent, and reduction components such as formaldehyde sulphoxylate orascorbic acid. Ammonium peroxydisulphate, also called ammoniumpersulfate, is preferably used.

The polymerization can be carried out using any technical method forpreparing an aqueous emulsion polymerization, employing non-ionic and/oranionic surfactants. Commercial emulsion products may also be used asneeded. The designs for the formulations and the reaction technology canbe utilized to obtain specific particle morphologies and reactivefunctionalities so that the PA can match the PU prepolymer/dispersionand/or PUA dispersion to give good film properties. Preferably, thepolymerization is carried out with the previously mentioned monomers andis initiated with radical initiators. In one embodiment of the presentinvention, the mixture of monomers pre-emulsion and the initiatorsolution are respectively fed into a reactor over a defined period oftime, such as 0.8 to 6 hours, preferably 3.5 hours. The initiatorsolution may comprise an initiator and water. The pre-emulsion comprisesmonomer mixture, surfactant/emulsifier and water. The polymerizationtime span is dependent on the reaction conditions, such as temperature,initiator type and dosage, monomer dosage (solid content) and thereactivity of the monomers.

Emulsion polymerization is generally conducted at temperatures of about55° C. to about 90° C., preferably 60° C. to 85° C., and more preferably75° C. to 80° C. After the completion of the polymerization reaction,the polymer emulsion is allowed to cool down to ambient temperature.

The obtained aqueous polymer emulsion has an average particle diameterof 30 to 300 nm, preferably 40 to 90 nm, more preferably 50 to 80 nm

The PUA dispersion made according to the present invention can be usedfor preparing coating compositions.

Additional ingredients of the coating composition include, but are notlimited to, stabilizers, colorants, pigments, dispersants, surfactants,paraffins, waxes, UV light stabilizers, rheology modifiers, mildewcides,biocides, fungicides, and other conventional additives. Colorants andpigment dispersions, when used, are typically added in amounts up toabout 15% by volume of the total composition.

In the present specification, the technical features in each preferredtechnical solution and more preferred technical solution can be combinedwith each other to form new technical solutions unless indicatedotherwise. For briefness, the applicant omits descriptions of thesecombinations. However, all the technical solutions obtained by combiningthese technical features should be deemed as being literally describedin the present specification in an explicit manner.

Examples I. Raw Materials

Materials used for preparing the PUA hybrid dispersion Function Chemicalnature Abbreviation Polyol Polypropylane glycol (Mw = 1000) PPG1kPolypropylane glycol (Mw = 2000) PPG2k Poly(butanediol adipate) (Mw =2000) PBA2k Polycarprolactone (Mw = 2000) PCL2k Polyethylene glycol (Mw= 400) PEG400 Polytetrahydrofuran (Mw = 2000) PTMEG2k IsocyanateIsophorone diisocyanate IPDI bis(isocyanatomethyl)cyclohexane ADICatalyst for Dibutyltin dilaurate DBTDL PU prepolymer DispersingDimethyolpropionic acid DMPA improving agent Chain extender1,4-butanediol BDO 1,2-propanediamine PDA Neutralizing Triethylamine TEAagent Ammonia NH3•H2O Surfactant Sodium dodecylsulphate SDS MonomerMethyl methacrylate MMA Butyl acrylate BA Acrylic acid AA Hydroxyl ethylmethacrylate HEMA 2-ethylhexyl acrylate 2-EHA Styrene St Otherfunctional Diacetone acrylamide DAAm monomer Acetoacetoxyethylmethacrylate AAEM Crosslinker Adipic acid dihydrazide ADH InitiatorAmmonium persulfate APS pH buffer Sodium bicarbonate NaHCO3

II. Synthesis Processes Synthesis of PUA1

-   (1) Putting 70 g PPG1k, 30 g PPG2k 10 g PEG400, 0.12 g DBTDL    catalyst into a three-necked flask, stirring and heating the flask    to 115° C. under N₂ purging and 10 g DMPA was then added to the    flask until the system became homogenuous and clear;-   (2) Adding 50 g IPDI into the flask when the temperature of the    reactant reaches to 75° C.;-   (3) Keeping the reaction for 120 min at 75° C.;-   (4) Adding HEMA into the flask and continuing the reaction for 0.5 h    at 75° C.; cooling the temperature to 65° C.;-   (5) Adding 100 g MMA and 20 g BA into the flask, stirring for 5 min    to obtain a clear solution;-   (6) Dissolving 1 g DAAm and ammonia in water and putting the    solution into the flask that contains PU prepolymer, and stiffing    for about 30 minutes at 80° C.;-   (7) Adding 20 g BA into the flask;-   (8) Adding 0.4 g ammonium persulfate (APS) into the flask    separately, and stirring the reactant for 1 h at 80° C.;-   (8) Filtering the dispersion with 100-mesh filter cloth and taking    the product as PUA1 dispersion.

Synthesis of PUA2

-   Under otherwise identical reaction conditions to PUA1, the procedure    involve: 100 g PPG1k, 100 g ADI, 30 g MMA and 10 g BA.

Synthesis of PUA3

-   (1) Putting 182.5 g PPG2k, 156 g PBA2k, 0.5 g DBTDL catalyst into a    three-necked flask, stiffing and heating the flask to 120° C. under    N₂ purging and adding 24.5 g DMPA into the flask until the system    became homogenuous and clear;-   (2) Adding 119 g IPDI into the flask when the temperature of the    reactant reaches 80° C.;-   (3) Keeping the reaction for 150 min at 80° C.;-   (4) Lowering the temperature to 55° C. and adding 36 mL MMA into the    flask, continue to stir for 0.5 h;-   (5) Adding 16 g TEA at 55° C. and stirring for 10 min;-   (6) Pouring the above prepolymers into 1200 mL de-ionized water    under vigorous stirring;-   (7) Adding 12 g propane diamine into the dispersion as chain    extender;-   (8) Taking 200 mL the dispersion into a 500 mL flask. Adding DI    water, sodium hydrogen carbonate, MMA monomers as well as ammonium    persulfate into the flask separately, and stiffing the reactant for    2 h at 75° C.;-   (9) Filtrating the dispersion with 100-mesh filter cloth and taking    the product as PUA3 dispersion.

Synthesis of PUA4

-   Making PUA4 under otherwise identical conditions as PUA3, except the    initial temperature for dissolving DMPA was 130° C. and the reaction    temperature was 95° C. The final temperature of prepolymer prior to    dispersing was 40° C. The polyols include 169 g PPG2K and 169 g    PBA2K.

Synthesis of PUA5

-   Making PUA5 under otherwise identical conditions as PUA3, except the    initial temperature for dissolving DMPA was 130° C. and the reaction    temperature was 95° C. The final temperature of prepolymer prior to    dispersing was 40° C. The polyols include 154 g PPG2K and 184 g    PBA2K.

Synthesis of PUA6

-   The synthesis procedure was similar to that for PUA4 except for the    polyol type and reaction temperatures. The detailed conditions were:    Using 338 g PCL2K as polyol. The initial temperature for dissolving    DMPA was set at 125° C. The reaction temperature was 90° C. Before    dispersing, the temperature was cooled to 60° C.

Synthesis of PUA7

-   Making PUA7 under otherwise identical conditions as PUA6, except the    monomer diluent was 40 g styrene and adding 0.4 g DAAm during    emulsion polymerization,

Synthesis of PUA8

-   Making PUA8 under otherwise identical conditions as PUA6, except the    monomer diluent was 40 g MMA and adding 0.4 g DAAm during emulsion    polymerization,

Synthesis of PUA9

-   Making PUA9 under otherwise identical condition to PUA3 except that    the initial temperature for dissolving DMPA was 85° C. instead of    120° C. for PUA3 and MMA was added together with polyol at the    beginning of the reaction.

Synthesis of PA1

-   (1) Charging the four necked flask with 24 g de-ionized water, 0.05    g APS and 0.26 g SDS surfactant; purging the reactor with N₂ for 20    min and then heating to 70° C. to initiate the reaction;-   (2) Feeding pre-emulsion containing 71 g of de-ionized water, 0.25 g    of NaHCO₃, 2.5 g of SDS surfactant, 0.4 g of APS initiator and    monomer mixture containing 74 g BA, 25 g MMA and 1 g AA.-   (3) Adding pre-emulsion over 120-150 min while maintaining the    70° C. reaction temperature. Adding 2.5 g DAAm when the remaining    pre-emulsion reached the volume of 25 mL;-   (4) Cooling to 45° C. and adding 2.3 g ammonia over 15-20 min

Synthesis of PA2

-   Dow commercial product E3808, copolymer of MMA, and BA, with Tg of    −25° C.

Synthesis of PA3

-   Dow commercial product E2468, copolymer of MMA, and BA, with Tg of    −15° C.

Synthesis of PA4

-   Dow commercial product E3188, copolymer of MMA, and BA, with Tg of    +50° C.

Synthesis of PA5

-   Dow commercial product BZ05-157, copolymer of MMA/ST/BA/EHA/MAA,    with Tg of +50° C.

Synthesis of PA6

-   Dow commercial product HS01-24, same composition to BZ05-157 except    one percent of DAAm was copolymerized, with Tg of +50° C.

Synthesis of PA7

-   Dow commercial product SF-230, copolymer of MMA/BA/MAA and one    percent of AAEM, with Tg of +5° C.

III. Examples

-   The blend samples were prepared by blending PUA and PA emulsions    following the recipe in Table 1. Blending is under stiffing only    with solids of PUA and PA being 40% and 50%, respectively. The    volume of each emulsion is 15 mL. ADH crosslinker was added as    solid.-   Cold-blended PUD and PA, as Comparative Example 1, was also listed    in the Table, it was prepared by blending, simply under stiffing, a    commercial PUD product, Bayer PR-240 of solid of 40 wt %, with PA2    in 1:1 volume ratio.

TABLE 1 Examples PUA PA ADH/g 1 PUA1 2 PUA2 3 PUA3 4 PUA4 5 PUA5 6 PUA67 PUA7 8 PUA8 Comp. 1 PUD PA2 Comp. 2 PUA9 Comp. 3 PA1 Comp. 4 PA2 Comp.5 PA3 Comp. 6 PA4 Comp. 7 PA5 Comp. 8 PA6 Comp. 9 PA7  1b PUA1 PA1 0  2bPUA1 PA1 0.02  3b PUA1 PA1 0.04  4b PUA1 PA1 0.06  5b PUA2 PA2 0  6bPUA3 PA3 0  7b PUA3 PA4 0  8b PUA7 PA7 0  9b PUA8 PA5 0 10b PUA8 PA50.05 11b PUA8 PA6 0

IV. Performance Test 1. Temperature Effects Comparative Example 2 vsExample 3

-   DMPA particulate was seen collected on the wall of the flask and the    solution of prepolymer at the end of synthesis is turbid or milky in    Comparative Example 2. In contrast, in PUA3 the solution was clear    and no particulate DMPA was seen in the flask.

2. Latex Film Preparation

-   The films were prepared by casting certain amount of dispersion into    a petri dish and let dry for two weeks at room temperature.    Generally, after one week of drying, the film was peeled off the    petri dish to dry the other side for one week.

3. Mechanical Properties

The mechanical properties i.e., the tensile strength and elongation ofthe latex films were measured using a Gotech-AI 7000M Universal TestingMachine with a crosshead speed of 200 mm/min. The experiments wereconducted at room temperature. Rectangle specimens of 80 mm×10 mm(length×width) free standing film with around 1 mm thickness were used.An average value of at least three replicates of each sample was taken.

4. The mechanical properties of films in Example 1 through 8, i.e. PUA1through PUA8 were summarized in Table 2. Comparative examples 3 to 9were listed in Table 3.

TABLE 2 Examples Tensile strength (MPa Elongation (%) 1 3.2 520 2 9.4303 3 44 680 4 22 1024 5 27 912 6 22 1050 7 32 700 8 25 700

TABLE 3 Examples Tensile strength (MPa Elongation (%) Comp. 1 — — Comp.2 — — Comp. 3 0.9 2000 Comp. 4 0.6 1800 Comp. 5 1.5 1100 Comp. 6 — —Comp. 7 — — Comp. 8 — — Comp. 9  1.55  663

By comparing Table 2 and Table 3, PUA films of Example 1 to Example 8showed significantly higher tensile strength than PA films of Comp. 1 toComp. 9. The tensile strength for PUA ranged from 3.2 MPa to 44 MPs. Forthe contrast, the strongest PA film had only 1.55 MPa tensile strength.The clear film formed from PUA samples showed high tensile strength andhigh elongation. Such performance well exceeded the performance oftypical EWC emulsion (about 1.0 MPa in tensile strength). For PA inComparative Examples 6, 7 and 8, the PA films cannot form film bythemselves at room temperature without using organic solvent as filmforming agent. The use of film forming agent can give rise toenvironmental concerns.

TABLE 4 Examples Tensile strength (MPa) Elongation (%) 1b 1.5 1500  2b 3500 3b 4.3 560 4b 6 332 5b 6.96 390 6b 7.7 700 7b —* —* 8b 10.6 421 9b12.6 233 10b  15.4 315 11b  17.1 313 *Not available

Those PA samples which could not form film at ambient temperature couldinstead form continuous film by blending with PUA emulsions. Themechanical performance of the blend samples were summerized in Table 4.

As shown in Table 4, Examples 1b through 4b, one can adjust the PUAmechanical properties of the latex films prepared from Example 1 withADH cross-linking agent to reach a satisfactory mechanical performance.Moreover, the properties can be tailored in a broad range by simplyadding various amount of ADH cross-linking agent. Example 9b and 10balso demonstrated the effect of crosslinking. With ADH, both tensilestrength and elongation performance were enhanced. The original PAexamples Comp. 6 to Comp. 9 cannot form film due to its high Tg. Afterblending with PUA, they can form film with superior tensile strength, asdemonstrated in Examples 7b through 11b. The original PA2 dispersion hasvery high elongation value but low mechanical strength. After blending,the mechanical properties of the blend film of Example 5b showed betterbalance in both tensile strength and elongation than each individualcomponent of Example 2 and Comp. 4.

Surprisingly, it was found that the clear film of Inventive Example 6bfrom Example 6 showed both high tensile strength and high elongation.The high modulus can be retained in their blend sample, being as high as7.7 MPa. The elongation was as high as 700%. Such performance wellexceeded the performance of typical EWC emulsion (about 1.0 MPa intensile strength). In such blend sample, no cross-linking agent was usedand the PU component accounts for only about 25 wt % of the totalweight, indicating the low cost and high efficiency in improving themechanical strength.

5. Storage Stability of Example 1b to 11b

Stability of five PUA/PA blend samples (Example 1b to 5b) and PUD/PAdispersions (cold blend, Comp. 1) was evaluated through heat-ageing at50° C. for 10 days. In all cases, no aggregation was observed fromPUA/PA dispersions after 10 days of ageing. As contrast, the PUD/PAdispersion (Comp. 1. did show some gelation and increase in viscosity.The higher stability of the PUA/PA system than PUD/PA system is thoughtto be derived from the better compatibility between PU phase and PAphase in the PUA/PA system.

6. Film Formation and Clarity Properties of Example 1b

PUA1/PA1 inventive hybrid dispersion (Exp. 1b) produced a film withsuperior clarity of 5 (5 is the best score and 1 is the worst score),while the clarity of PUD/PA blend (Comp. 1) was 2.

7. Film Formation of Example 7b to 11b, with High-Tg PA

Comp. 6 to Comp. 9 alone could not form continuous film at roomtemperature because of its high Tg. Example 7b to example 11b (the blendof high Tg PA and PUA) with the volume of 1:1 could form continuousfilms and the films are of good clarity, which showed that PUA are wellcompatible with high Tg PA in the present invention.

8. Coating Performance of Example 7b

The blend of PUA3/PA4 (Example 7b) was used as clear coat in woodcoating. The performance was summarized in Table 5. It was found thatthe clear film showed good water resistance and 50% alcohol resistance.No plasticizer was used in the formulation, so the formulation was zeroin VOC.

TABLE 5 Performance of the clear film formed with PUA3/PA4 (Exp. 7b) in1/1 blend ratio* Pendulum hardness 2 days 50% 100% PU (50° C.) + PencilWater alcohol alcohol (wt %) MFFT^(a) 4 h 26 h 1 day(RT) hardness^(b)resistance^(c) resistance^(c) resistance^(c) 25% <0° C. 75 94 107 B 5 52 *No plasticizer; ^(a)Minimum Film Formation Temperature ^(b)Hardest toSoftest: 4H, 3H, 2H, H, F, HB, B, 2B, 3B, 4B, 5B, 6B; ^(c)Best = 5;Worst = 1.

1-7. (canceled)
 8. A polyurethane/acrylic hybrid dispersion preparedaccording to a process comprising the following continuous steps: i)adding at least one polyol into a reactor; ii) addingdimethylolpropionic acid (DMPA) simultaneously with step i), or afterstep i) but before step iii), as a water dispersibility enhancing agentat a temperature of from 115° C. to 140° C. to obtain a homogeneoussolution; iii) adding at least one polyisocyanate at a temperature offrom 75° C. to 95° C. and stirring until NCO content reaches a constantvalue to prepare a polyurethane prepolymer; iv) adding at least oneacrylate monomer, at least one styrenic monomer, or a mixture thereof,as a diluent to the polyurethane prepolymer, at a temperature of from40° C. to 65° C.; v) adding a neutralizing agent; vi) dispersing thepolyurethane prepolymer in the presence of the acrylate monomer, and/orthe styrenic monomer of step iv); and vii) adding at least oneethylenically unsaturated nonionic monomer, and co-polymerizing ittogether with the acrylate monomer, and/or the styrenic monomer of stepiv), to get the polyurethane/acrylic hybrid dispersion.
 9. A coatingcomposition comprising the polyurethane/acrylic hybrid dispersionaccording to claim
 8. 10. The polyurethane/acrylic hybrid dispersionaccording to claim 8, wherein the polyurethane/acrylic hybrid dispersionis cold-blended with a polyacrylate dispersion under agitation to form apolyurethane/acrylic hybrid dispersion/polyacrylate dispersion blend.11. The polyurethane/acrylic hybrid dispersion according to claim 10,wherein the polyurethane/acrylic hybrid dispersion and/or polyacrylatedispersion are modified by copolymerization with diacetone acrylamide oracetoacetoxyethyl methacrylate; and adipic acid dihydrazide, ascrosslinker, is added into the polyurethane/acrylic hybriddispersion/polyacrylate dispersion blend.
 12. The polyurethane/acrylichybrid dispersion according to claim 8, wherein the acrylate monomer isselected from the group consisting of acrylic acid, methyl(meth)acrylate, ethyl acrylate, butyl acrylate, hexyl acrylate,2-ethylhexyl acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate, glycidyl methacrylate, and combinations thereof.
 13. Thepolyurethane/acrylic hybrid dispersion according to claim 8, wherein theat least one polyisocyanate is a diisocyanate.
 14. Thepolyurethane/acrylic hybrid dispersion according to claim 13, whereinthe diisocyanate is selected from bis(isocyanatomethyl)cyclohexane,hexamethylene diisocyanate, isophorone diisocyanate, and combinationsthereof.
 15. The polyurethane/acrylic hybrid dispersion according toclaim 8, wherein the at least one polyol consists of polyether polyols,polyester polyols, polycarbonates, or mixtures thereof.
 16. Thepolyurethane/acrylic hybrid dispersion according to claim 8, wherein theat least one polyol consists of a combination of polyether polyol andpolyester polyol.
 17. The polyurethane/acrylic hybrid dispersionaccording to claim 8, wherein step vi) of the process further comprisesadding a chain extender.
 18. The polyurethane/acrylic hybrid dispersionaccording to claim 8, wherein the polyurethane/acrylic dispersion isfree of organic solvent.
 19. The polyurethane/acrylic hybrid dispersionaccording to claim 8, wherein the polyurethane/acrylic hybrid dispersionis free of particulate dimethylolpropionic acid (DMPA).